A digital fluidics cartridge, such as a droplet actuator, may include one or more substrates to form a surface or gap for conducting droplet operations. The one or more substrates establish a droplet operations surface or gap for conducting droplet operations and may also include electrodes arranged to conduct the droplet operations. The droplet operations substrate or the gap between the substrates may be coated or filled with a filler fluid that is immiscible with the liquid that forms the droplets. Reagents and other liquids are used in digital fluidics cartridges. However, it can be difficult to introduce reagents into the droplet operations gap without generating air bubbles and/or foam. Further, often quantities of reagent are stored for long periods of time (e.g., many months) before being used in a digital fluidics cartridge. However, during storage the concentration of the reagent can change to unacceptable levels due to, for example, water vapor transmission loss of the packaging. Therefore, there is a need for new approaches to managing reagents for use in digital fluidics cartridges, such as droplet actuators.